Process for casting slabs



oct.. 20, 1942. L, ROGERS ETAL 2,299,111

PROCESS FOR CASTING SLABS Filed Feb. 12, 1940 3 Sheecs-Sheec` l ATTORNEYS Oct. 20, 1942. ROGERS ET AL 2,299,111

PROCESS FOR CASTING SLABS -Fled Feb. l2, 1940 3 Sheets-Sheet 2 rr'n f rn I/ 1 77 INV NT R5 Mime/b ATTORNEYv 09.291942. H. L. GERS -m. 2,299,111

PROCESS FOR CASTING SLABS Filed Feb. l2, 1940 3 Sheets-Sheet 3 INVENTORS i; 1. .T m;

ATTORNEYS Patented Octr 20, 1942 Homer L. Rogers and Gayle B.- Price, Dayton, Ohio, assignors, by mesne assignments, to said Price Application February 12, 1940, Serial No. 318,461

3 Claims.

This invention relates to precast concrete slabs.

One object of the inventionY resides in the process of making precast slabs whereby slabs of great strength or rigidity and `of predetermined size may be accurately and economically produced.

Another object resides in the process of casting concrete slabs, whereby one surface of the slab is given a very smooth finish so that it may be used in building construction without additional surfacing.

Another object of the invention resides in the process of making precast concrete slabs in which concrete mixture is 'added to a form and around a passage forming tube or tubes, and involving the vibration of the form to remove air from the reinforcement and with respect to the sides of the form in which the concrete is cast. f

Another object of the invention is' the provision of apparatus for making precast slabs, adapted to be used in carrying out the process above referred to.

Other objects and advantages of the invention will be apparentfrom the following description, the appended claims and the .accompanying drawings.

In the drawings, in which the preferred embodiment of the apparatus and process of the present invention have been illustrated as adapted for the production of precast reinforced concrete slabs for use in building floors, roofs, etc.:

Fig. 1 is a perspective view of a portion of a building floor formed from precast concrete slabs madeV in accordance with the present invention;

Fig. 2 is a transverse sectional view through one of the slabs;

Fig. 3 is a section on the line 3-#3 of Fig. 2;

Fig. 4 is a perspective view of a series of theslabs arranged to provide a floor and a ceiling, and showing how the slabs are assembled;-

Fig. 5 is a top plan view of a portion of the slab series shown in Fig. 4;

Fig. 6 is a section on the line 6--6 of Fig. 5;

Fig. 7 is a side elevation of a form in which the concrete slabs are cast, and showing the supporting means for the form;

Fig. 8 is a transverse section through the form on the line 8-8 of Fig. 7;

Fig. 9 is an end view of the form showing the upper straps removed;

Fig. 10 is a longitudinal section through a portion of the end of the form and taken on the line III- I0 of Fig. 9;

Fig. l1 is a perspective view of an end portion of the form and its support; and

Fig. 12 Ais an enlarged sectional view corresponding to Fig. 10 and illustrating the pretensioning ofthe reinforcing rods.

Referring more particularly to the drawings, like parts being designated by the same reference numerals in the several views, I0, II and I2 designate portions of precast concrete reinforced slabs or beams such as may be made in accordance with the 'process and by means of the apparatus as will hereinafter be described. Such slabs may be arranged side by side, to form a building wall, being shown supported at their opposite ends to provide a floor or roof of a building and to provide the ceiling of a room below the floor or roof. The slabs may be carried at one end on a flat surface such as a leveling strip I3 arranged on a metallic, masonry or 'concrete foundation I4, the opposite ends of the slabs being carried in a similar manner.

The particular form of slab-herein shown, and as set forth in our copending application Serial No. 318,460 filed February 12, 1940, for Cast slabs, comprises a concrete body I6 of general rectangular cross section form, see Figs. 2 and 3, having reinforcing rods I1, I8 and I9 extending longitudinally of the slab near its lower side, with additional reinforcing rods 20 and 2| preferably embedded in the concrete near the upper side of the slab. Longitudinal passages 22 of large diameter compared to the thickness of the slab extend longitudinally from onek end of the slab to the other, these passages, as shown, having a diameter considerably in excess of onehalf the slab thickness to give a total void space of from 40% to 50% of the slab. The slab is preferably twice as--wide as it is thick, and with that proportioning, there are preferably two passages 22 spaced a suitable distance apart and from the sidewalls of the slab.

The lower side 24 of the slab is smooth, having curves 25 at its edges, these curves merging into side surfaces 26 which are adapted to be arranged in abutting relation with the corresponding portions of adjacent slabs. The top surface 21 of the slab is -somewhat shorter in width than the bottom surface, so that the upper side surfaces 28 of adjacent slabs are spaced apart to provide a channel to which grout is applied so that when the grout is set the slabs will be held firmly one to another. The side surfaces 28` are provided with longitudinally extending grooves I 29 so that the hardened grout willy be securely interlocked. to the adjacentjslabs.

4face of the slabs. 1 shows a Wood flooring 38 laid on Wood strips 33 set forth in our copending application Serial No.

318,462, filed February 12, 1940, for Building c'onstruction. With the supported ends resting on flat leveling strips |3, these end portions will be flush with one another but the several slabs may not be of exactly uniform strength and may not extend exactly even with one another when ilrst placed in position on the leveling strips. To level the slabs at their middle or unsupported points, nuts 3| threaded on bolts 32 are placed in the channels between adJacent slabs, beingy moved longitudinally along these channels from one end of the slabs, the nuts 3| being of such size that they engage the grooves 23 and are held against turning in these grooves. The bolts, when applied to the channels between adjacent slabs, cany plates 34 which slide over the upper surfaces of the slabs. With several bolts arranged at suitably spaced intervals along the length of the channels, the plates 34 are arranged to extend transversely of the length of the slab, as indicated in dotted lines in Fig. 6 and as shown in the center of Fig. 5. A frame comprising angle irons 35 and 35 connected at their ends by connecting plate 31, see Fig. 5, is then moved down against the top of the slabs, so as to extendtransversely of the sla-b length, the width of the plates 34 being small enough so thatvthey will be received between the angle iron webs as the frame is placed in position. The plates 34 are then raised and turned 90 so that they will rest onthe horizontal webs of the angle irons and the bolts 32 are turned with a wrench so that one lslab is pulled vertically with respect to an adjacent slab that may 4be at a slightly different level, as the nuts 3| are brought tight against the upper parts of the grooves 23 of the slabs. All of the slabs may thus be brought to a flush relationship with one another.

After the slabs have been leveled and all of the bolts 32 tightened, the space between adjacent slabs is filled with grout level with their upper surfaces, suitable grout retaining plates being placed across the ends of the slabs. After the grout is hardened, the bolts 32 are unscrewed from the concrete, leaving the nuts 3| in place, and the angle iron frames are taken on. 1f desired the threaded holes which are left in the concrete when the bolts 32 are removed may be filled with grout, although they may remain if a wood flooring is to be applied to the upper-sur- The left-hand portion of Fig.

secured by bolts 40 that thread into the threaded passages in the concrete left when the bolts 32 are removed.

in accordance with the present invention the concrete slabs are cast in a form shown in Figs. 7 to 11 in the shape of an open top horizontally extending trough having internal dimensions in accordance with the size of the slab produced. The form comprises a smooth metal plate 42 which extends continuously along the length of the form, and which is preferably made of heavy vsheet metal having upwardly turned side walls 43 providing smooth curved fillets 44 at each of the lower corners. On each side of the plate 42 are side walls 45 and 45, preferably in the form of channel irons, each channel iron having a metal plate 41 secured to its inner side above the location of the wall portions 43 of the bottom plate. There may be a small distance between the lower ends oi' the plates 41 and the upper ends of the wall portions 43. On each plate 41 isa semi-circular .rod 4 3 which forms the longi- .tudinally extending groove 23 in the slab. The

member. As shown in Fig. 8, the left-hand end j of the bar 43 is riveted to the lower web of the side channel 45 and at its right-hand end it extends under the channel 46 and is provided with a hole registering with a hole location in the lower web of this channel so that a headed pin 5| may be slipped up through the registering holes and a wedge 52 driven in a slot in the pin, thus clamping the bar 43 securely against the lower side of the channel. 'I'he wedge may be very readily driven out of place and the pin Il removed to separate the bar 43 from this channel. As previously mentioned, the next adiacent Ibar 43 is riveted or bolted to the lower wall of the channel 43 and has a detachable connection to the lower Iwall of the channel 45. The side members of the form are carried on a plurality of spaced pedestals 54, the bars 43 supporting the bottom plate 42 in its proper position to conan air hose.

st itute the lower wall of the trough or form.

. One end of the form is closed by an end plate 55 which has a. pair of small openings 55 receiving pins 51 which are welded to and project from the outer sides of the channels 45 and 45 as shown in Figs. 9 and 11, these pins 55 being slotted to receive wedges 58 -which secure the end plate 55 against the vends o1' the side ,channels and the end of the bottom plate 42. A similar plate 55 may be carried in a similar manner at the/ opposite end of thev form so that the length of the form will determine the 'length of the slab to be cast in it.

In the plate 55 are large holes 50 and 5| having a diameter corresponding to the size of the passages that are cored in the slabs. These holes 53 and 5| receive the ends of tubes 53'which are of greater length than the slab to -be cast, and serve to exactly position the ends of the tubes. In the embodiment of the invention herein illustrated, these tubes are inflatable rubber tubes of the character disclosed in the patent to Lindas No. 1,949,650. Where such rubber inflatable tubes are employed, the normal uninflated tube diameter is considerably less than the diameter oi.' the openings 50 and 5| in the end plates. The tubes, when inflated, expand uniformly in diameter throughout their effective length, and shorten in length at the same time. The opposite ends of the tubes are provided with valves 55 which may be readily coupled to and inflated from The tubes are applied and then subjected to suiilcient pressure to bring the walls of the tube securely against the holes'50 and 5| and the pressure supply is then cut ofi.

The tubes are applied to the forni from one end by passing them through the reinforcing steel structure which is first laid in the form, this structure comprising the reinforcing rods |1, I3 and I3 which act in tension in the finished product, and additional longitudinally extending reinforcing rods 20 and 2| which are especially desirable for transportation purposes when the forms are carried in an inverted position. These several rods are interconnected to one another at spaced intervals along the length of the form by means of wires 61, connected 'preferably by weld- A ing to the longitudinally extending rods and having a cross sectional form corresponding to the size of. the rectangle dening the total cored area. The distance between the horizontally extending portions ot the wires 61 will thus correspond to the inflated diameter of the tubes 53.v and the sidesof the tubes 63 will contact with the vertically extending portions of these wires, which are of suiiicient rigidity to hold the tubes from spreading apart within the form.

After the reinforcing structure and the core tubes are in place in the form, straps 68 are placed across the'top of the form at suitable spaced intervals along its length, these straps having a readily detachable connection so that they may be quickly applied and removed. As shown in Fig. l

8 one end of the strap 68 is provided with a clamping plate 69 which is pivotally carried by a connecting bolt 1 2 so 4that it may be turned to the position shown in Fig'. 8 and extend under the upper flange ofthe channel 45,l being held up against the channel by a spring 10 which bears against a thrust washer above the nut 1I on the bolt. A spacing washer 13 is interposed between the clamping plate 69 and the strap 88 as indicated. When the clamping plate 69 is turned 90 from the position shown the strap 88 may be pulled upwardly and removed. At the other end of the strap 68 ls a clamping plate 14 pressed upwardly by a spring 15 that bears against a nut onfthe lower end of a bolt 16 which supports the clamping plate for turning movement below the extended end of the strap 68. A handle 11 is iixed to the plate 14 and extends at 90 to the length of this plate so as to extend parallel to the channel 46 when the clamping plate yis held in clamping position by the spring 15. The handle may be turned'into the dotted Vline position shown in Fig. 8 to turn v The tensioning' nuts 85 are tightened so as to the clamping plate 14 and release itfrom the channel iron and-to permit the withdrawal of the strap 58. y

The clamping plate 68 carries two hooks 18 extending through holes in the clamping plate and reaching down-so as to hook under the upper rods 20 and 2| and pull the reinforcing structure upwardly. Springs 19 urge the hooks 18 in an upward direction but permit a person' Ygrasping the handled upper ends of the rods to press them downwardly and release them from or. engage them with the rods of the reinforcing structure. These hooks hold the reinforcing structure up in its proper position .within the form and also held the tubes 63 up against locating pins 88 iixed on the strap 68 and engaging the upper sides of the tubes 63 so as to position these tubesl at the proper distance from the sides of the form and at afdesired height in the form. The tubes, being hollow, tend to rise in the concrete mixture applied to the form, but the pins 80 hold them down in their intended positions.

When the several straps 68 are in place and engaged with the reinforcing structure and with the upper sides of the tubes, the several parts are held in their intended positions throughout the length of the form.

The rods l1, I8, and I9 end in threaded lugs 82 having head portions 83 which may be welded to the ends of the rods, and threaded extensions 84, the plates having openings located opposite the threaded extensions 84 and of such size as to receive tensioning nuts 85 adapted for `threaded engagement with the extensions 84.

stretch the rods and thus pretension them to give a predetermined initial elongation, the nuts being turnedby aytorque wrench 86 having a square stud 81 engageable with the sockets 88 of the tensioning nuts 85. The handle of the torque wrench may be turned and the amount of torque applied to the nuts 85 shown by sultable indicating means or by presetting the torque wrench to give the required amount of torque in order that the rods may be pretensioned to some point below their elastic limit. "I'he degree of pretensioning is preferably such that the finished slabs, -when supported at their opposite ends, will be prevented from 'sagging in their middle portions, and will extend horizontally when supporting their own weight from their opposite ends. This pretensioning of the rods also increases the effectiveness of lthe reinforcement vwhen the slab deilects under heavy load. The

upper rods 28 and 2| may be tensioned in the same way although that is ordinarily unnecessary since they oier suiiicient strength to permit carrying the slabsin an inverted position without applying excessive or cracking strains from their own weight.

In those cases where the length of the slab is shorter than the length of the form a plate 55 may be used at one end of the form, while the other end of the form is provided with a plate that ts between the inner sides of the side members of the form and rests on the bottom plate 42, as shown-in Fig. ll. Side bars 9| are welded to the outer side of this plate and project along the inner sides of the side channels. The bars 9| are provided with a series of holes 92 adapted to receive 'a transversely extending .holding bar 93 Awhich engages against the ends of the side channels and thus holds the plate 90 at apredetermined distance from the en`d of the form. A spacing tube 94 holds the ends of the side bars 9| in properly spaced relation. This plate 90 is provided with openings 68 and 6I and with additional openings for the reception of the tensioning nuts 85, and when the tensioning4 nuts are in place engaging the ends of the rods, the plate 90 is securely held at its proper distance from the plate 55 at the other end of the form to give a slab of the required length.

With the form assembled, the reinforcement and core tubes 63 in place, and the tubes infiated, the form is ready to receive the concrete mixture, it being understood thatthe surfaces of the form to which the concrete mixture is applied are iirst oiled so that the concrete, when set, can be readily separated from the metal partsf of the form. The concrete mixture is poured or shoveled into the form, until it comeslevel with the top of the form, the concrete mixture being a suitable mixture or mass to provide a hard strong compound formed by concretion or coyalescence ofthe particles such, for example, as a mixture of one part cement and five parts of a mixture of sand and gravel, thoroughly mixed together with water.

After filling the form it is then supported for vibratory movement and rapidly vibrated for a short time. For this purpose the form is raised up from the pedestals 54 by, and supported on, lifting trucks 95 having pneumatic tires-9,.an axle frame 91, a load supporting bar 98 xed to Ithe frame 91, and a bifurcated handle 99 also pedestal 54 and the formls thus supported from centric weight mounted on motor driven shaft Vwhich rotates on a horizontal 'axis parallel to the truck axle, the eccentrically mounted weight causes a vibratory movement at rather highspeed, shaking the form vertically with an amplitude of the order of one-eighth of an inch. The amount of air.pressure to which the tires 96 oi' the trucks are inflated is properly chosen with respect to the length of the slab, longer slabs beout the pins ll. When the nuts Il are unscrewed the rods remain bonded throughout their length to the concrete'and the head portions 83 prevent any relative slipping or stripping of the concrete along the rods. The two sides of the form are then pulled horizontally awayfrom one another and the 'plate 42 is taken from the top of the form. This may leave a. small :Bn-like projection where the concrete has filled in just between the ing vibrated with less air pressure in the tires,

while if only a comparatively short slab is to be made, and the weight to be shaken-is therefore much less, the tires may be inflated harder so that the degree of movement imparted to the form will be about the same regardless of the length of the form. The air pressure in the tires of course depends upon the size of the tires themselves, and may be varied through a wide range.

In casting concrete beams ytwenty feet in length and having a width and thickness of the order of twelve inches and 'six inches respectively, the air pressure in the tires may be of the order of twenty pounds. The vibratory movement of the concrete causes air bubbles to rise rapidly in the concrete mixture, and causes the mixture to entirely fill allof the crevices and come into intimate contact with all surfaces of the form, tubes, reinforcement, etc., resulting in a very strong product because of the elimination of the air bubbles and causing a very smooth surface on thoseportions of the slab that engage the metal bottom and side members of the form. This vibratory movement continues for a few minutes, or until air bubbles cease to come rapidly from the top of the mixture, and the handles 99, of the trucks are then raised to lower the form on the pedestals again in order that the trucks may beused for another form. Raising the handles swings the supporting bars 98 of the truck towards the pedestals and in a downward direction so that the trucks may be readily wheeled out from below the form.

After the air has been removedy from the concrete mixture, the hooks 18 are released from the reinforcement, the handles 11 turned, and the straps 68 removed from the top of the form. The top surface of the concrete is then smoothed and leveled ofi with the top of the plates 41 which preferably extend a little distance upwardly from the top of the side channels 45 and 46, and any depressions such as those .caused by the pins 80 and the hooks I8 are filled up with concrete, preferably by a hand operation. The concrete isthen permitted to stand in the form for several hours or until the concrete sets hard enough to permit the form tobe removed.

After the concrete has set the tubes 63 are deflated and pulled out of the concrete. Of course unscrewed, and the plates 55 removed by driving wall portions 43 of the plate 42 and the ends of l -the plates 41, and this fin is removed by hand.

The concrete is then permitted to dry and harden until the slab is in condition to be transported.

The forms, as will be quite apparent, are capakble offbeing quickly assembled and disassembled and oi' being readily handled without loss of time to produce reinforced concrete slabs of different desired lengths of uniform strength and cross sectional form, and with an accurate and reliable positioning of the core passages and the re- 1 inforcing structure.

While the process and form of apparatus herein described constitutes preferred embodiments of the invention, lt is to be understood that the invention is not limited to this precise process and form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in thev appended claims.

What is claimed is: .1. The process of making a precast concrete slab comprising locating a tube in a trough fonn,

adding concrete mixture to the form and around the tube, vibrating the form to remove air bubbles from the upper exposed surface of the concrete mixture while supporting the form pneumatically, and controlling the air pressure of the pneumatic support in accordance with the length of mass of the' slab.

2. The process of making a precast concrete reinforced slab comprising applying a set of reinforcing rods to the upper portion of an open top horizontal form and a set of lower reinforcing rods to the lower portion of the form, pretensioning one of such sets against the ends of the form so that the pret'ensioned set has a substantially different initial stress than the other set, locating opposite end portions of an inflatable tube in the form ends and inilating the tube, filling the form with concrete, vibrating the form while the upper surface of the concrete is freely exposed to the air for the removal of gas `from the concrete throughout the length of the form, allowing the concrete to harden, deilating and removing the tube, releasing the rods from the form ends and removing the form.

3. The process of making a precast concrete reinforced slab which inherently has an upward curve in a. longitudinal direction when the slab is free from stress comprising applying reinforcing rods tov upper and lower portions of an open top horizontal form the bottom of which is straight longitudinally of the form, pretensioning the lowerrods against the form ends, locating opposite end portions of a tube in the form ends, i'llling the form with concrete, vibrating the form while the upper surface of the concrete is freely exposed to the air, allowing the concrete to harden, releasing the rods from the form ends, and removing the form.

HOMER L. ROGERS.

GAYLE B. PRICE. 

